[lustre-discuss] lfs data_version $filename

[DEGREMONT Aurelien]

Hello

This is feature is primarily used by HSM, internally, but is not limited to.
data_version is a number computed from each OST objects the file is made of.

Two different values for data_version mean the file content has changed. 
Two identical values mean the content is identical. There is not 
relationship like older or more recent. There is no order between values.
Values from 2 different files cannot be compared. This has no sense.


Aurélien


Le 12/04/2018 à 17:28, E.S. Rosenberg a écrit :
> This is just a guess - could it be related to ZFS backends? Allowing 
> for snapshots etc.
>
> On Thu, Apr 5, 2018 at 10:53 PM, Ms. Megan Larko <dobsonunit at gmail.com 
> <mailto:dobsonunit at gmail.com>> wrote:
>
>     Greetings List!
>
>     What is the number from the command "lfs data_version $filename "
>     telling me?
>
>     I do not see "data_version" documented in lfs -h, man lfs, nor in
>     lustre manual..
>
>     I do know that if I have a zero-length file my robinhood scan of
>     my Lustre mount point indicates that "lfs get_version" failed.  As
>     the file in-question is zero length, I have no problem with this
>     (other than lines in my robinhood lustre.log file making it large).
>
>     I understand that Lustre File System uses three numbers to
>     validate data integrity.  How does the number returned from "lfs
>     data_version" come into play?  What reference number is that one?
>
>     Thank you in advance for the education.
>     Cheers,
>     megan
>
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